Wireless devices can be tested either in real environments or by using a radio channel emulator (also called a fading emulator or a radio channel simulator). Radio channel models are provided to the radio channel emulator to simulate the real environments. Since tests performed in real environments are typically cumbersome and subject to uncontrollable phenomena, the radio channel emulator is a preferred solution. The radio channel emulator can emulate many radio channel dimensions including the spatio-polarimetric. Antenna characteristics of the wireless device may also be modeled. A radio channel emulator can include a finite impulse response (FIR) filter, which generates convolution between a radio channel model and an applied signal. The FIR filter includes a series of delays, multipliers, and adders to modify the applied signal and provide a simulated output signal representative of a real environment. The radio channel model may be adapted to represent different real environments by modifying the series of delays and coefficients associated with the multipliers. One method of using the radio channel emulator requires direct coupling to the antenna ports of the wireless device with coax cables.
However, some wireless devices to not have available coax connections between their antennas and antenna ports. Additionally, with cellular wireless communications the cell sizes are getting smaller and the utilized bands are getting higher in frequency. This trend will continue with the coming 5G cellular systems. Base stations will be smaller and include more integrated units. Both base station vendors and their antenna manufacturers have indicated that the coming smaller base stations may not have coax connections for their antennas. When the coax connections are not available, a multi-probe anechoic chamber (MPAC) may be required. However, MPACs are expensive and require large floor areas. A typical wireless device such as a Long Term Evolution (LTE) base station or LTE wireless user equipment (UE) may require an MPAC utilizing over 100 square meters of floor space.
For at least the aforementioned reasons, there is a need for improved methods for alleviating the need of an MPAC or direct coax cable coupling to antenna ports of a wireless device-under-test (DUT).